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metalmagpie
08-18-2015, 11:08 AM
I'm working on an upgraded welding table. Since I often need to plug in angle grinders or other power tools, I plan to install some 117VAC outlets on the table, and plug them into the wall behind the table. I'm wondering about connecting the table to earth ground.

In other words when I connect the welder's ground clamp to a part clamped on the table, that should be at earth potential, right?

I know if this were a hi-fi I'd be generating a big fat ground loop, which would be bad design. It just seems weird to me to think about running conduit and jboxes and not grounding them. Of course, the outlets themselves will be grounded.

metalmagpie

lakeside53
08-18-2015, 11:12 AM
In reality.. use a steel outlet boxes correctly grounded to the incoming power cord and you are ready to go. For the currents you are concerned with, Conduit is a legal ground if installed correctly. Oh.. it's not legal to use metallic conduit unless it is grounded. The conduit is grounded via the j-boxes.

If you are worried use a #6 wire with lug (typical nec "equipment ground') and ground the table to your ground spike.

There is no issue with "ground loops". Ground in electrical distribution systems are multiple and redundant

Don't assume you welder "ground" is really " ground" for electrical safety purposes. Any current from the welder will return via the welders ground return lead. Does your welder even work of you leave that clamp off but the work is "grounded". if so... run a FAT (sized to the welder) ground lead back to the panel, just incase you forget to clamp on the welder lead. Somehow I doubt it will work without the welder "ground" clamp on.

boslab
08-18-2015, 11:45 AM
It probably wouldn't hurt but I found all the wire under your feet was a problem, so I got some recoil units mounted to the ceiling for 110v and air, keeps them out of the way, and if they are under your table you need to change the flex on the tool to heat resistant, I melted a few before I got the message
Mark

danlb
08-18-2015, 01:40 PM
The welder's ground clamp is rightly called the "work" lead. It's purpose is to provide a return path for the welding current (from the stinger/gun). It is not the same as the 110v (or 220v) ground.

I would NOT ground the table. I'd isolate the outlets from the table. Use the principle of "double insulated".

My reasoning; If you ground the table, it becomes a very likely return path for any accidental contact with a live electrical wire. It's also very likely that you will be touching that table when you accidentally cut through the power cable on your grinder.

Disclaimer: I have no idea what NEC says about grounding a welding table.

Dan

PStechPaul
08-18-2015, 02:14 PM
I found this, which states that the welding table must be separately grounded:
http://www.thefabricator.com/article/arcwelding/staying-grounded


According to American National Standards Institute (ANSI) Z49.1, "Safety in Welding, Cutting and Allied Processes," the workpiece or the metal table that the workpiece rests on must be grounded. You must connect the workpiece or work table to a suitable ground, such as a metal building frame. The ground connection should be independent of or separate from the welding circuit connection.

boslab
08-18-2015, 02:58 PM
As above to what they say, however the steelwork on buildings are often welded to and on, the electrical earth is connected to the steelwork, if however the 0volt of the welding set became detached I suppose there would be a risk of the earth leads of the tools becoming the 0 volt line, if you see what I mean, that would be bad!, so what they said applies!, my tools are not connected to the bench by the earth, I'm guessing that with the right circumstances the bench COULD end up at 240 volts also very bad, it would trip every breaker, the earth leakage trip etc over here but that's with our wiring
Do the safe thing, I retract wouldn't hurt as bad
Mark

JoeLee
08-18-2015, 07:00 PM
My welding table is ground........

JL...............

http://i911.photobucket.com/albums/ac317/JoeLee09/Broaching%20Pulley%20Bore/Image001_zps0682b4b2.jpg (http://s911.photobucket.com/user/JoeLee09/media/Broaching%20Pulley%20Bore/Image001_zps0682b4b2.jpg.html)

J Tiers
08-18-2015, 08:58 PM
The welding return cable is not grounded.....

So no issues with double grounding should exist. Ground the worktable and go on with life

If your welder is from 1902, I have no idea how it is set up..... but any modern or reasonably modern welder is isolated, for reasons that are obvious as soon as you consider welding on structural steel, and what that would do ground-wise if there were a grounded return wire.

CalM
08-18-2015, 10:20 PM
My welding table is ground........

JL...............

http://i911.photobucket.com/albums/ac317/JoeLee09/Broaching%20Pulley%20Bore/Image001_zps0682b4b2.jpg (http://s911.photobucket.com/user/JoeLee09/media/Broaching%20Pulley%20Bore/Image001_zps0682b4b2.jpg.html)

That must be a " TIG ONLY" table, or the photo was taken moments after the table was placed in service. Even brazing flux leaves marks ;-)

macona
08-18-2015, 10:49 PM
The output from a welder is isolated from the mains, so the ground lead is not at earth ground. The only connection to earth ground may be though a couple foil capacitors inside the welder to shunt away HF from getting into the machine.

RichR
08-18-2015, 11:14 PM
That must be a " TIG ONLY" table, or the photo was taken moments after the table was placed in service. Even brazing flux leaves marks ;-)

Nah, he lays down cardboard prior to welding to keep that surface pristine.

PStechPaul
08-18-2015, 11:55 PM
It's a J-B welding table :rolleyes:

The output winding of the welder transformer should be well isolated from ground and the primary. The transformer in my cheap welder appears to be a "split bobbin" type which offers very good isolation at the expense of high leakage inductance and poor voltage regulation, but that's a desirable feature for welding because it limits the maximum current to a safe value. If the transformer is layer wound there may be considerable capacitance between primary and secondary which could provide enough current for a mild shock. If the table is not grounded, it presents a hazard if the operator touches earth ground with another part of the body.

tc429
08-19-2015, 12:06 AM
My welding table is ground........

JL...............


and Blanchard ground at that! :)

BigMike782
08-19-2015, 08:56 AM
My guess is it started out as a 4" thick top and he likes to use his blanchard grinder.:D

JoeLee
08-19-2015, 10:01 AM
No, actually it started out as a 1 1/4" thick piece of plate, blanchard ground on each side with a finish dimension of just over 1 1/8" thick.
I made it back in like 2005 and the picture was taken last year. I mostly TIG, if I should MIG weld on it I have a piece of galvanized sheet that fits over it to protect it from splatter.

Now back to the subject............. I never ground to the table, intentionally anyway. There have been times when I've forgotten to ground my work and the clamp was clamped to the table, I'll usually find that out pretty quickly as I'll hear a snap when the part arc itself to the table to make it's connection.

I believe my Miller Synchrowave has floating ground. I've never checked it with a continuity meter to see if the ground wire is isolated from the electrical outlet ground. I assume it is. I have gotten RF bites on my arms if I should touch them on the table when I'm welding if I ground through the table.

JL.....................

J Tiers
08-19-2015, 10:03 AM
... There have been times when I've forgotten to ground my work and the clamp was clamped to the table, I'll usually find that out pretty quickly as I'll hear a snap when the part arc itself to the table to make it's connection.
...
JL.....................

Which has ZERO to do with the table being, or not being, grounded. :D

kf2qd
08-19-2015, 11:30 AM
The welding supply uses a transformer. The primary and the Secondary are isolated from each other. If it is then rectified then that is a very important feature. Because the 2 halves are isolated the output of the DC welder can be connected positive ground or negative ground and with the table tied to earth ground it just limits what max voltage could appear on the workpiece. I have played with ungrounded secondaries on a transformer and the voltage difference to ground can do some wild and crazy things. And it can give you a pretty good jolt, though very low current. Most of the time there is sufficient ground through concrete to keep that from happening, but if you have a nicely painted floor you might want to have a earth ground from the table . Ungrounded tables can act like a capacitor and give you an occasional jolt of shock therapy. The larger the flat surface the more capacitance.

The other thing that the earth ground helps with is getting rid of electrical noise that can bother computers and radios, TVs...

JoeLee
08-19-2015, 03:14 PM
Which has ZERO to do with the table being, or not being, grounded. :D


I know that.......

JL...................